Unseasonable latewood and incrusted pits are the cause of drying in Pinus halepensis and P. eldaricainfested with Matsucoccus josephi

Mendel, Z. and Liphschitz, N. 1988. Unseasonable latewood and incrusted pits are the cause of drying in Pinus halepensis andP. eldarica infested with Matsucoccus josephi.-J. exp. Bot. 39: 951-959.A study was made of the effects of Matsucoccus josephi (Insecta: Homoptcra: Margarodidae) on (a) water transport in Pinus halepensis, using a basic fuchsin solution and (b) the structural changes of the xylem of Pinus halepensis, P. brutia andP. eldarica using a scanning electron microscope.Examinations were carried out in artificially and naturally infested plants. Transport of the fuchsin dye was arrested below the affected zone of heavily infested shoots, but reached the shoot apex through sparsely infested segments or via segments heavily infested with the first larval stage. Heavily infested stem sections of P. halepensis and P.eldarica were characterized by narrow pits and incrusted pit membranes. In non-infested shoots and those infested with first or early second-scale larvae in both these species and heavily infested P. brutia shoots, there were typical earlywood pits with wide pit apertures and thin membranes. It is suggested that blocking of water ascent in P. halepensis and P. eldarica starts when female second-instar larvae complete their development and only when population density is relatively high. Therefore, it is considered that the accelerated drying of the growth of P. halepensis and P. brutia is directly related to the narrowing of the pit apertures, which resembled those of latewood pits although produced early in the season. The absence of changes in the xylem of heavily infested P brutia may explain why this species tolerates a high density of M. josephi. The structural modification of the xylem caused by the scale may be related to imbalance in plant growth hormones which are either transmitted with the insect saliva or formed in the plant by salivary enzymes.